EFFECTS OF THIDIAZURON, NAPHTHALENEACETIC ACID, DARK INCUBATION AND GENOTYPE ON SHOOT ORGANOGENESIS FROM MALUS LEAVES

Adventitious shoots were induced from sections of in vitro-derived leaves of several Malus genotypes using a regeneration medium supplemented with four levels of thidiazuron (TDZ) (1, 2, 3 and 4-mu-M) and three levels of naphthalene acetic acid (NAA) (2.7, 5.4 and 8.1-mu-M). Optimum shoot regeneration of 'Mclntosh' leaf explants was obtained in a medium containing 2.7-mu-M NAA and 4-mu-M TDZ. The influence of dark incubation on shoot induction indicated that one week of darkness was sufficient for organogenesis. Increasing TDZ concentration (5, 10, 15 and 20-mu-M) in the medium had varying effects on the frequency of regeneration of several genotypes including 'Royal Gala', 'Gala', 'MacSpur', 'Dayton', 'Golden Delicious', and M.7. Significant differences between the six genotypes were observed for regeneration frequency with an average of 11% for M.7 to 100% for 'Gala'.